The continued dependence on fossil fuels for energy production and the environmental effects of combustion of such fuels is commonly associated with the increasing climate change observed globally. The combustion of such fuels produces carbon dioxide (CO2), a so-called greenhouse gas, which was previously generally released into the atmosphere. Because of the environmental effects of greenhouse gases, resulting for instance in global warming, there is ongoing research into the reduction of emission of CO2 into the atmosphere. One method for reducing the emission of CO2 into the atmosphere is for instance the capturing and storage of CO2. The classical method used in CO2 capture is reactive absorption followed by thermal regeneration of the absorbent liquid (Figueroa et al., International Journal of Greenhouse Gas Control 2008, 2(1), 9-20). Amines used to capture CO2 from gaseous streams react to form water soluble compounds, which degrade on heating to release the CO2. Monoethanolamine (MEA) is a regularly used base for the capture of CO2, with efforts being put into developing other possibilities. However, the high energy input used for regenerating the absorbent liquid makes this method less favourable. Aside from this method, there is continuous work being done on newer technologies for the capture of CO2 like use of gas membrane contactors (Powell et al., Journal of Membrane Science 2006, 279(1-2), 1-49), chilled ammonia process (Darde et al., International Journal of Greenhouse Gas Control 2010, 4(2), 131-136), formation of carbonates (Favre et al., Journal of Molecular Catalysis B: Enzymatic 2009, 60(3-4), 163-170), and use of ionic liquids (Hasib-ur-Rahman et al., Chemical Engineering and Processing: Process Intensification 2010, 49(4), 313-322).
However, after the capture of CO2, there is still need to sequester or use the CO2, in other words to keep it away from the atmosphere. Before the present invention, the capture and storage of CO2, with sequestration in geologic forms has attracted attention (Figueroa et al., International Journal of Greenhouse Gas Control 2008, 2(1), 9-20). Also methods of converting the captured gas into methane, concrete and even in the use of sugar production have been explored by others.
WO-A-2010/151787 discloses CO2 absorption by a carbonic anhydrase solution and using the resuling bicarbonate ions to facilitate growth of algae. However this document does not disclose separation of the rich absorbent liquid into two fractions, one of the fractions having a higher enzyme concentration than the other.
Ramanan et al. (Bioresource Technology 2010, 101, 2616-2622) disclose CO2 sequestration using Chlorella sp. and Spirulina platensis algae. This document, too, does not disclose separation of the rich absorption liquid into two fractions, one of the fractions having a higher enzyme concentration than the other. Additionally, Ramanan et al. are silent as to recycling.